The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Modern day power assisted braking systems used on passenger automobiles (i.e., cars and trucks) typically make use of a brake booster to assist providing a pressurized fluid flow to the brake calipers of the vehicle when the operator depresses the brake pedal of the vehicle.
Typically the brake boost assist system includes a ball screw nut which is driven by an electric motor. In one embodiment, shown in FIG. 1, a driver applies a force on a brake pedal (not shown) which is transferred to a coupling element 1 along the direction of arrow A. A sensor within the brake boost assist system 2 (not visible in FIG. 1) detects movement of an input rod 3 caused by the pedal movement. An electronic control unit (“ECU”) of the vehicle determines an appropriate control strategy. A motor (not visible) operably associated with the brake boost assist system 2 receives a signal from the ECU during a braking action, which signal is partly dependent on a sensed stroke of the brake pedal. The motor drives a belt 4 which drives a pulley 5, which in turn drives a ballscrew nut (not visible). The ballscrew nut drives a ballscrew 6 in an axial movement in accordance with arrow B. This causes movement of a piston located within a casing or housing of the brake boost assist system 2. The piston is driven in an axial motion toward a fully extended position, which changes the hydraulic pressure in a master cylinder of the vehicle. When the piston is driven axially toward its fully extended position, it provides a maximum pressurized fluid flow to the brake calipers of the vehicle to help in braking the vehicle.
In the rare event that DC power to the ECU is suddenly lost, a condition may develop in which the hydraulic pressure developed within the housing of the brake boost assist system acts on the piston and drives it rapidly and abruptly back to its fully retracted (i.e., “home”) position. During this retracting movement the electric motor is driven in the opposite rotational direction by the reverse rotational movement of the ballscrew 6. Since there is little resistance provided by the motor when it is driven rotationally in the reverse direction by the ballscrew, there is a possibility that the ballscrew may be driven with significant force by its associated components (e.g., motor, pulley, etc.) such that its sudden stop may result in significant force being exerted on an interior wall of the housing. This may give rise to a risk of fracturing the housing or otherwise damaging the ballscrew. Accordingly, it would be highly desirable to somehow detect, in real time, when a power loss condition has arisen and the brake boost assist system has lost power, and to provide some mechanism for dynamically braking the motor of the brake boost assist system to prevent damage to the system.
An additional consideration is when a brake boost assist system is disconnected from DC power while the motor of the system is spinning. In this rare instance, generated voltage from the motor may damage components in the brake boost assist system. If the processor happens to be in a sleep state, for example because of a temporary power loss condition, the processor will not be able to take any action to control the motor, and thus potential damage to other components of the brake boost assist system may be incurred. Thus, some mechanism is needed to sense when the brake boost assist system has lost DC power, and to ensure that the processor controlling the brake boost assist system is activated so that the processor can take the necessary action to assert control over the motor and avoid damage to other components of the system.